Soil stripping and replacement for the rehabilitation of bauxite-mined land at Weipa. III. Simulated long-term soil organic matter development

Long-term trends in soil organic carbon (C) and nitrogen (N) under current and alternative rehabilitation practices at Weipa were simulated using the CENTURY model. After 100 years, predicted organic C in the surface soils (0-20 cm) of each treatment had risen to new dynamic equiliPbria. Since the 'passive' pool of recalcitrant organic C, which occupied 47% of organic C, changed little over the simulation period, the new equilibria differed according to initial organic C content. Most organic matter recovery occurred in the 'slow' fraction, although the greatest rate of change occurred in the 'active' C pool, which stabilised within 50 years at levels similar to the native forest. Similarly, 'slow' C accumulated in all treatments to new equilibria which were similar to that in undisturbed forest soil. The main difference between treatments was in the predicted time until a stable equilibrium in the 'slow' pool was reached: between 90 and 160 years depending on the soil stripping and replacement operation used. Successful development of new equilibria was highly sensitive to the amount of legume N-2 fixation in the system and also to the severity of C and N losses during fire events. Reasonable agreement was found between simulated organic C accumulation and that observed in surveyed rehabilitation of up to 15 years of age (r(2) = 0.67 for freshly replaced soils, r(2) = 0.72 for soils stockpiled before respreading).